chore: init Cyrene_v2 project structure and DevDocs

- Create directory structure for backend, frontend, deployment, tests
- .gitignore with DevDocs/ excluded from version control
- DevDocs: 00-overview, 01-cross-platform, 02-dev-constraints
- DevDocs decisions: 002-communication (NATS), 003-plugin-architecture
- DevDocs modules: ai-core analysis, gateway analysis

.gitignore

@@ -0,0 +1,52 @@
+# 开发设计文档（本地参考，不入库）
+DevDocs/
+
+# 环境变量与密钥
+.env
+models.json
+*.local
+*.pem
+*.key
+
+# 构建产物
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+backend/cmd/*/main
+backend/cmd/*/cyrene
+cyrene
+
+# Go
+backend/vendor/
+
+# 前端
+node_modules/
+dist/
+.vite/
+
+# Python
+__pycache__/
+*.pyc
+.venv/
+venv/
+*.egg-info/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# 系统
+.DS_Store
+Thumbs.db
+desktop.ini
+
+# 日志
+*.log
+
+# 临时文件
+tmp/
+temp/